The present invention pertains to a polycrystalline cubic boron nitride (PcBN) cutting insert, and especially a coated PcBN cutting insert. The coated PcBN cutting insert attaches to a support with the support and PcBN cutting insert comprising a coated PcBN cutting tool. The coated PcBN cutting tool is useful for the removal of material from a workpiece, e.g., chipforming machining of a workpiece.
Heretofore, artisans have used PcBN cutting tools for the removal of material from a workpiece, e.g., chipforming machining of a workpiece. Patent documents, such as for example, U.S. Pat. No. 7,455,918 B2 to Gates, Jr., et al. (assigned to Kennametal Inc.), provide some examples of these PcBN cutting inserts. In this regard, U.S. Pat. No. 7,455,918 B2 describes via Inventive Heat Nos. 3 and 4 (see Columns 13-13), as well as Col. 19, line 63 through Col. 21, line 37, coating processes for a substrate that includes PcBN. Further, U.S. Pat. No. 5,503,913 to König et al. describes a PcBN cutting tool. U.S. Pat. No. 7,476,063 to Wickman et al. describes a PcBN cutting tool wherein a PcBN layer forms the face of a cutting tool. U.S. Patent Application Publication No. US2005/0123366A1 to Goudemond et al. describes a PcBN cutting tool that appears to have a body with pockets wherein each pocket receives a compact such as a PcBN compact. U.S. Pat. No. 6,737,178 to Ota et al. describes a PcBN cutting tool wherein a base contains pockets that appear to carry a PcBN substrate. There is a coating on the PcBN substrate. U.S. Pat. No. 6,090,476 to Thysell et al. appears to show a PcBN cutting tool.
A coating scheme (i.e., coating layer(s)) applied via CVD to a cobalt cemented tungsten carbide substrate exhibits a tensile stress. The presence of the tensile stress is detrimental to the adhesion of the CVD coating scheme. Heretofore, some have used a post-coating blasting treatment to reduce the tensile stresses in the coating scheme or to change the stress to compressive stress in the coating scheme.
As one example, U.S. Pat. No. 5,372,873 to Yoshimura et al. (assigned to Mitsubishi Materials Corporation) discloses shot peening the coating scheme on selected surfaces wherein the substrate is a cobalt cemented tungsten carbide, which exhibits a surface layer of cobalt enrichment. The result of shot peening is a change in the stress condition of the coating. In this regard, this patent shows that the shot peening process may be applied locally to parts of the cutting tool, for example to the rake surfaces, so that the residual tensile stresses in the primary coating thereon are lower than those tensile residual stresses in the primary coating on the flank surfaces of the cutting tool. Further, this patent also shows a shot peening treatment applied so that the residual stresses in the primary coating of the rake surfaces of the cutting tool are compressive, and that the residual stresses in the primary coating of the flank surfaces are tensile.
As another example, U.S. Pat. No. 5,374,471 to Yoshimura et al. (assigned to Mitsubishi Materials Corporation) discloses shot peening a coating layer on a substrate wherein the shot peening is effective to treat only the rake surfaces. The substrate is a cobalt cemented tungsten carbide, which exhibits a surface layer of cobalt enrichment.
A coating scheme (i.e., coating layer(s)) applied via CVD to a cermet substrate exhibits a tensile stress. United States Patent Application Publication No. US2006/0127671 A1 to Park et al. discloses the use of wet blasting as a post-coating treatment of a coating on a cemented carbide substrate, as well as cermet substrate. The wet blasting process uses alumina particles, which have a size between 10-300 μm, water slurry. There is a reduction in the tensile stress or a conversion to compressive stress in the outer coating layer due to the wet blasting. Specific coating schemes include an alumina coating with titanium carbide/titanium nitride layer(s) on top of the alumina layer.
Another consequence of a post-coating treatment such as wet blasting is a smoothening of the coating surface. United States Patent Application Publication No. US2006/0204757 A1 to Ljungberg discloses a two-step wet blasting post-coating treatment for a coating scheme comprising a TiCxNy coating layer and an α-Al2O3 coating layer. The substrate is a cobalt cemented tungsten carbide material. These treatments show the affect due to variations in impingement angle and pressure. This treatment results in a smoother coating surface and a reduction in tensile stress or a conversion to compressive stress. U.S. Pat. No. 5,861,210 to Lenander et al., which discloses a Ti CxNyOz layer on alumina (see Col. 2, lines 30-43), discloses that it is known to vary the blasting parameters (see Example 1, Col. 4, line 48 through Col. 5, line 11) to achieve different results.
United States Patent Application Publication No. US2007/0009763 A1 to Littecke et al. discloses a wet blasting post-coating treatment for a coating scheme comprising a TiCxNy coating layer and an α-Al2O3 coating layer. The substrate is a cobalt cemented tungsten carbide material. This treatment results in a smoother coating surface and a low tensile stress TiCxNy coating layer and a smooth α-Al2O3 coating layer.
Each one of United States Patent Application Publication No. US2007/0298281 A1 to Andersson et al. and United States Patent Application Publication No. US2007/0298282 A1 to Andersson et al. discloses a wet blasting post-coating treatment for a coating scheme comprising a TiCxNy coating layer and an α-Al2O3 coating layer. The substrate is a cobalt cemented tungsten carbide material. This treatment results in a low tensile stress TiCxNy coating layer and a smooth α-Al2O3 coating layer. The stress condition is different between the rake surface and the flank surface.
In addition to wet blasting, some have used dry blasting to reduce the tensile stress in the coating. For example, U.S. Pat. No. 6,884,496 to Westphal et al. discloses the basic benefits of dry blasting a coated cutting insert wherein there is an increase in the compressive stress. See Col. 2, lines 42-67.
There should be an appreciation that some of the blasting operations remove only a small portion of the coating layer. U.S. Pat. No. 7,531,213 to Bjormander pertains to a coated cutting tool insert wherein the post-treatment (preferably blasting or brushing) removes the outermost coating layer only on the edge-line and on the rake face.
Some of the above patent documents show a cutting insert useful for the removal of material from a workpiece, e.g., chipforming machining of a workpiece, wherein the coating scheme has been subjected to a post-coating treatment. This post-coating treatment has resulted in a reduction of the tensile stress or a conversion of the stress to compressive stress in the coating layer(s). This post-coating treatment has resulted in a smoothening of the outer coating layer. However, many of these patent documents show a cutting insert, which possesses a cemented carbide substrate or in one case, a cermet substrate. These patent documents do not disclose the actual implementation of a post-coating treatment to a coating that has been applied to the surface of a PcBN body (or PcBN cutting insert) resulting in a reduction of the tensile stress or a conversion of the stress to compressive stress in the coating layer(s), as well as a smoothening of the outer coating layer.